Modern surgical procedures have evolved into precisely managed cooperation between the surgeon and the supporting team of anesthesiologist and nurses. Careful observation is maintained over such mechanisms as respiration, blood pressure, pulse rate, EKG and temperature. Any aberration in these signs is noted so that necessary corrective action may be taken, or the surgical procedure modified or aborted, if necessary, to protect the patient's condition.
During surgical procedures fluid and electrolyte losses always occur via lungs and skin, characterized as "insensible loss", and not directly measurable, except by sensitive change in body weight. Sudden losses of fluid can occur in the form of hemorrhage. At present, this type of loss can only be estimated by weighing sponges and pads and by measuring the blood in the suction bottle. Slower losses of fluid and electrolyte, primarily sodium and chloride ions, occur when abdominal and thoracic surgery is in progress as nonvisible secretions by the mucus membranes lining these cavities. During extensive procedures such as with vascular and traumatic problems, fluid and ion losses can be rapid and massive, as much as 1000 cc being lost per hour, and not measurable save by a sensitive weight determination. When signs of circulatory abnormalities appear, the surgeon and anesthesiologist must guess as to the state of the patient's hydration, and treat with intravenous solutions accordingly. Serious overhydration is the commonest result, when, in fact, cardiac and central nervous system abnormalities per se require specific recognition and direct treatment.
A somewhat similar case of fluid overload can occur during a urologic operation, transurethral resection of the prostate gland, or tumors of the bladder, where irrigating fluids containing no electrolytes are used to distend the bladder and prostate for effective vision. These fluids may easily enter the patient's circulation, leading rapidly to overhydration, overload of the circulation and dilution of the electrolytes--all serious problems with short- and long-term consequences. This may happen more frequently when residents are being trained to perform an operation. Continuous sensitive monitoring of the patient's weight and, therefore, water content, would call immediate attention to the hazard at its onset, and an operation would be discontinued safely.
In view of the above, it is apparent that a system for automatically and accurately tracing the patient's loss or gain in weight in real time during surgical procedures would be a valuable adjunct in increasing the safety of such procedures. The present invention is directed to this aspect of surgical management.